With increasing population densities, the height and size of buildings are increasing. To this end, steel structures are used in most large high-rise buildings.
In the event of a fire, however, large high-rise buildings pose a high risk of personal injury due to toxic gases, and the strength and bearing capacity of steel structures thereof are decreased due to heat and may thus be vulnerable to collapse owing to the weight of the building. With the goal of solving these problems, methods of forming a refractory coating layer on the outer surface of such a steel structure have been adopted.
Specifically, low-carbon steel for use in constructing steel structures has a critical temperature of about 540° C., and the bearing capacity of the structures is decreased to about 60% at temperatures higher than the critical temperature. Hence, in order to maximally prevent the bearing capacity of the steel structures from decreasing and personal injury from occurring in the event of a fire, the steel structures are subjected to refractory coating. Also, concrete structures are required to resist explosive spalling and degradation of concrete materials attributable to heat for a predetermined period of time. Furthermore, refractory coating is performed to ensure that the original properties of the concrete structures are retained even after the fire is extinguished.
Conventional refractory adiabatic coating materials are composed mainly of asbestos and rockwool, asbestos being a known carcinogen, of which the worldwide use thereof has almost completely stopped, and inorganic fibrous rockwool generating large amounts of dust upon construction, undesirably creating a poor construction environment for workers and contaminating the surrounding environment.
Rockwool-based refractory coating material is favorable in terms of low specific gravity and superior fire resistance, but requires proficiency in order to construct it at an appropriate density so as to satisfy desired fire resistance and strength, and entails difficulties in maintaining a stable slurry (suspension). Furthermore, problems such as peeling of the coating material and scattering of inorganic fibrous rockwool may occur over time after construction.
In order to overcome the above problems, compositions containing a variety of expanded natural minerals, such as vermiculite and perlite, have been developed for preparation of the slurry (suspension), but the expanded natural minerals have numerous surface pores, making it difficult to control open pores by changing viscosity upon construction through spraying using the slurry mixed with water.
Hence, materials for solving the above problems are being developed and introduced, but most techniques emphasize initial adhesion, adhesive strength, etc., and methods of retaining durability or resistance to flames at high temperatures in the event of a fire for a predetermined period of time have not yet been devised.
Korean Patent Application Publication No. 10-2011-0108075 discloses a method of increasing heat resistance at high temperatures in the event of a fire using foamed ash and foamed perlite. Although this technique is based on a mechanism whereby an increase in temperature is delayed by the use of the foamed material, the foamed material has open pores and thus the effect of blocking heat is insignificant due to the presence of the pores.
Also, Korean Patent No. 10-0992888 discloses a method of using gypsum and waste concrete powder as industrial inorganic byproducts. However, this patent is based on a mechanism in which the pores inside the refractory coating material are controlled so as to block heat, rather than an improvement in heat resistance at high temperatures, and thus basic solutions for ensuring heat resistance are still lacking.